PorKen

This graph is even more striking. -8° ret vs. +2° adv. +24 rwhp (SAE) at 6500 rpm, with a small loss (~5) at the first torque peak. (Torque below 2000 is much lower, which is OK for a manual.)

The torque tipping point appears to be @ ~4150 rpm (for S3 cams).

PorKen

Acceleration, as you might imagine, is 'brisk', when shifted over 6000. (High Kibort-μ. )

Black car has a shift-light and a flat-shift kit, which works with the new torque peak perfectly. Green light, 6200 rpm, clutch in, 4800 rpm rev limit, clutch out, go go go, repeat.


I think the feeling of 'effortlessness' at high rpms is partly due to there is much less engine braking with this much retard. Much like driving a GT, it feels 'normal' to tool along at 4000 rpm. RPMs don't drop like a stone when you let off the gas briefly.

PorKen

I reckon the graph above shows well why advancing reduces max HP. Just a small reduction in torque at high rpm reduces the multiplication of rpm to HP.



I think I can go to '9'.

For more, the belt would have to be restrung, and the piston is getting very close to the valves.


EDIT: In hindsight, this isn't really true. There is still plenty of room for the valves. At least 15°, or two teeth.

Lizard928

Ken,
How many CAD does it actually take with stock cams before interference occurs?

PorKen

Don't know.

Lots of people, including me, have strung the belt one tooth (7.5°) off, plus whatever is set in the slot.

The Kibort famously says he skipped three teeth with S4 cams. >22.5°!

I would hazard 15° is 'safe', but I don't think I'll go over 9.


Note that the WSM/dial indicator 'zero', or what the 32V'r shows, is actually 2° advanced over the center of the cam key (straight up, like a 16V gear).

PorKen

Adjusted, engine spun with starter, remeasured, within 10 minutes of shutting off the engine, with the oil hot, and the coolant temp in the middle of the gauge, versus sitting at 37F/3C, the 5-8 does show -1° retard. (1-4 was the standard -2° retard.)

I'm quite sure that a very hot engine will add another 1° or more advance to both sides. Conversely, as the engine cools, it will retard quickly.

If you really, really, want to be spot on, the cams should be set with the engine as hot as possible. If not, the cold adjustment should be (at least) 1-4: -2°, 5-8: -1°, under the target hot measurement, especially if you are racing, or looking for consistent dyno results.

PorKen

The question now is, what is the change, if any, at high rpm?

rgs944

My belt is about a year old now and I want to get my timing dialed to what best suits me. Please offer any suggstions as the settings I should use. It is a Street driven S4 5 speed with x-pipe and very free flowing exhaust. I have no access to a dyno so I am looking for suggestions for my best chance for optimizing HP and TQ. I read through most of this thread but still do not know what would be best to set at. Most of the time I stay under 4000rpm's.

dprantl

This is good data. Next time I have the covers off, I am going for lots of retard since I have so much low end torque with the eaton. I should be able to pick up some more HP at the top. I'm thinking -8 deg on both sides will be good.

Dan
'91 928GT S/C 475hp/460lb.ft

PorKen

My current thinking is that (+2°) advance is good for throttle response, but a little worse for mileage. Zero (or -2°) retard is usually the 'best' setting overall for manuals. Higher HP from retard will be above 4000 rpm, though.


More advance or retard and you'll need to SharkTune to get good results. Less ignition advance for advance, more for retard. (If you depend on the knock sensors, there will likely be too much retard.) If you have already ST'ed the fueling, then more fuel may be needed overall, and especially at high rpms (more horses = more oats).

More retard lets the engine rev easier, and you'll find yourself rev'ving it higher*. Conversely, you get more engine braking with more advance.


I'm running +3° advance on my '86.5 auto, and it is very responsive, but only gets 14 mpg/city. (Needs 92 octane fuel, with a 91 octane EZ chip.)

-7° is a lot easier to adjust to, cold†. (Too bad I chose +10 to -9 when I designed the 32V'r...)

For retard to show gains, you'll need to advance the ignition timing, and you'll probably need more fuel, especially at WOT.

For my NA S3, I added roughly +0.75° ign per -1° cam below the 'tipping point' (<4500), and +0.5° above. (Trade signs for advance.)


* PKT recommended/required!
† When I get some time again, I'm going to standardize a high rev*, 'Black Edition' S300s chipset @ -7°. First, I'm going to try the retard on my auto, to see how it performs.

dprantl

Good to know. I have the ST2 permanently installed in my car, so modifying the fuel map and ignition timing is not a problem.

Dan
'91 928GT S/C 475hp/460lb.ft

mark kibort

good stuff, and thanks for the HP props! not only for my benefit, but for all those wanting to be "in the know" .

anyway, are you saying that you saw the 24hp gain for the retard to 8 degrees vs 2 adavance, PLUS timing changes? or was it a strictly cam timing change?

as i mentioned when i got the new cams (85 vs the Holbert cams that were basically GTcams), the 85 cams set at stock settings was about 8 degrees more advanced than the GT cam. (lets just call the holbert cams GT cams). when i retarded the timing at the track, after the car dynoed at 15hp less than before cam change, it woke it up at the track and changed the exhaust note, clearly heard on the in-car-camera footage comparison. i guess retarding the 85 cams got the same timing as the GT cams, at the expense of the exhaust cams being retarded , which isnt really that optimal.

yes, i was able to jump 4 full teeth and not hit, but that is expected, since the cams only move the valves, .2mm with 20 degree crank movement.. the valves try and chase the pistons, but never catch up unless you skip a couple of more teeth. my car ran with 3 teeth off, but it was the worse running car you could ever imagine! reset it and it was back to the races.

Cosmo Kramer

Ken, with running the Vortech supercharger and having lots of high rpm boost/hp and kind of lacking down low, do you thing advancing the cams would help boost the low end torque while letting the SC take care of the top end?

mark kibort

this is truely a remarkable took for what i will be using it for on the 6 liter friend of mine's street 928 that has run badly for many many years now. im thinking its cam timing. knocking, weird exhaust note, etc. Bill, do you have the porken tool so we can test the 6 liter cam timing. be interesting to see if that was the reason. poor cam timing. compression test looks a little like the passenger side is lower by about 10psi vs the driver side, but it could be chance. if its cam timing, that might be the issue.

if it was my race car, i would probably do both again. take the cam covers off and do it the old fashion way, and then verify with the tool. there was some variance with mine side to side. i forgot if it was due to he heads being shaved or something else. ill have to check my notes.

Bill Ball

Mark K:

Yes, I have the Porken tool. Use it all the time. Let me know when you want to look at this.